Ward’s and others comments on this remind me of an experience that I had at my
qth a few years ago. After what I thought was a direct hit on one of my
towers, we lost cable (no surprise there). Turns out that it was not a tower
hit, but rather a case of lightning coming in via the cable lines (which has
happened twice before). What was interesting was when the cable guy came out
he could not locate the cable splitter into which the cable feed from the
utility pole was connected. He also could not locate the clamp used at the
cable ground! Hmmm.... What happened to them?
I find them in two different places about 15’ away from the side of the house
where the cable feed was connected. I lost cable because of the surge that
literally blew out the splitter and cable ground (and the connection on the
utility pole). There was no clamp on the splitter it was just screwed into the
side of the house before it was literally “blown away”. Both the splitter and
the ground clamp (VERY flimsy) showed damage and black scorches on them. This
incident nicely illustrates what Ward and others are talking about.
I then watched him attach a flimsy hoseclamp for the cable ground, on its own
ground rod NOT connected to the house utility ground connection (equally
flimsy). I remarked on this and he said “that was the code”. I subsequently
went out and improved the ground. In another storm, lightning came via our
well pump and it had to be replaced. After the installation, the guy made a
solder connection on an extremely thin wire to make a “ground”. It was a cold
solder joint and completely useless. I pointed it out whereupon he resoldered
it. I then asked him about the ridiculously flimsy wire ground and he said it
was code. I was appalled.
I don’t know whether or not these two examples were up to code or not but if
they were then the codes here are grossly inadequate and guaranteed to cause
more damage in the future to my property (not that they care – they don’t live
here!). If they weren’t up to code then the cable company and the well
installer were either lazy or incompetent or both. A problem either way.
Moral of the story- be prepared to make BETTER ground connections than code –
it is your property and safety and the only person that will care about it is
you!
I use the Bronze heavy duty two hole compression clamps on the legs of each of
my two towers. Although they have taken multiple intense hits over the years,
including FIVE in one “storm from hell”, they have never been scorched or
loosened. I know that it is not the best ground possible, but mechanically it
has repeatedly stood the “lightning tests”.
73
Bob KQ2M
From: Ward Silver
Sent: Monday, October 16, 2017 12:56 PM
To: Billy Cox
Cc: Reflector
Subject: Re: [TowerTalk] Fwd: Grounding connection to tower legs
A quick reply - yes, the stainless steel shim clamps can be used *in
some circumstances* but my understanding from Polyphaser folks was these
are not to be used as primary grounding clamps for heavy conductors.
These are just to attach some kind of light-duty strap or wire (or
braid!) to a galvanized pipe, tube, or rod. For the main ground
connection that is intended to handle the lightning surge, you have to
use the heavy-duty clamps.
A good source of information is usually an electrician or tower
installer who knows what the local codes are and any special
circumstances that require particular hardware, coatings, etc.
73, Ward N0AX
On 10/16/2017 11:13 AM, Billy Cox wrote:
> Good Morning All, and I am reading along this with interest given past
> posts
> as to the what/where of properly using worm-gear type clamp products.
>
> Ward ... please note that some suppliers DO seem to suggest their use?
>
> http://www.polyphaser.com/products/grounding-and-bonding
>
> On the other hand, and from the daily calls/email here as to "can I do
> this or
> should we do that?" with various clamp products, there are many many
> design
> factors that really need to be properly considered with this topic.
>
> So given the various present unknowns here (clamp type, bandwidth,
> thickness,
> type of materials and so on) I can't fully agree or disagree with your
> statements
> as to the use of worm-gear clamps for such applications. But it is
> interesting ...
>
> Basically this topic comes down to risk management. And as one who in
> times
> past did things poorly and suffered the consequences in the form of
> canceled
> insurance, and extra work/time/investments to overcome the root causes
> ....
>
> I would suggest each person understand their specific risks, study
> appropriate
> sound technical information (such as Ward's book!) to decide what to
> do there.
>
> 73 de Billy, AA4NU
>
> Disclaimer if needed: Product Manager - Ideal Clamp Products.
>
> ------------------------------------------------------------------------
> *From: *"Ward Silver" <hwardsil@gmail.com>
> *To: *"Reflector" <towertalk@contesting.com>
> *Sent: *Monday, October 16, 2017 7:26:02 AM
> *Subject: *Re: [TowerTalk] Fwd: Grounding connection to tower legs
>
> > Why would the hose clamp blow apart? I have used this method for decades
> and have had multiple direct lightning strikes.
>
> The mechanical forces on a conductor carrying kilo-amp currents from a
> lightning strike can be extreme - many pounds per foot of conductor. (This
> is described by Ampere's Force Law.) That's why codes require ground
> conductors for lightning rods and antennas to be secured to a building or
> support structure. (This was news to me, too.)
>
> Basically, the conductor experiences a huge jerk which would destroy
> either
> the conductor or whatever is trying to secure it - like a hose clamp. So
> it would be more accurate to say that the hose clamp is not rated to
> withstand the force experienced by the ground conductor and is not blown
> apart by the current. It's the mechanical force.
>
> If hose clamps have been used and the tower has taken hits without
> damaging
> them, then the ground conductors are not for whatever reason carrying
> enough of the current pulse to generate damaging forces. Or maybe the
> configuration of the conductor was such that the force was weaker than it
> could be. i.e. - you got lucky :-)
>
> I'm no different in that I've used hose clamps over the years for similar
> applications and got away with it. No more. As long as we're in True
> Confessions mode, I've used braid from old coax (outdoors, even!) and
> soft-soldered strap and braid to ground rods. No more of that, either.
> Live and learn, especially now that I live back in the lightning zone
> (Missouri) with towers on a high spot.
>
> So the advice is just to use the right stuff for the job. It's not that
> expensive (a lot less than your insurance deductible, that's for sure) and
> has been engineered to minimize corrosion and handle the mechanical
> requirements of the application.
>
> I also got a question about CadWeld and those are great for ground
> electrodes but I would never use them on the tower itself. It may be
> possible to safely weld a connection to a tower but I wouldn't do it to a
> tubular load-bearing leg, not to mention the dissimilar metals
> involved and
> all that. I wouldn't want to weaken a cross-brace either, especially when
> there are other options designed for that exact application. Maybe someone
> with broadcast tower experience could weigh in on that. I repeat, for us
> hams, just buy the right stuff and and do what the manufacturer says.
>
> 73, Ward N0AX
> _______________________________________________
>
>
>
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